1. Field of the Invention
The invention relates to a communication system, and more particularly, to a synchronization method and related apparatus of a digital communication system.
2. Description of the Prior Art
In a conventional orthogonal frequency division multiplexing (OFDM) communication system, data are modulated with a plurality of sub-carriers, then a transmitter transmits OFDM symbols to a receiver in a series of data packets. As known by those skilled in the art, digital video broadcasting (DVB-T) and digital audio broadcasting (DAB) both correspond to the communication structure of the OFDM communication system. In DVB-T applications, in order to conform to the MPEG2 standard, a packet of 188 bytes first has to be scrambled and Reed-Solomon encoded into a packet of 204 bytes, and then the 204-byte packet is transmitted after being encoded, modulated, and subjected to inverse fast fourier transformation (IFFT). At this time, data in individual MPEG2 packets is scattered. Therefore, the receiving end has to recombine the received data for returning the 204-byte packet to the original 188-byte MPEG2 packet. Additionally, the receiving end has to execute the fast fourier transformation and demodulations, and detect a synchronization byte (SYNC byte) before Reed-Solomon decoding. After the above-mentioned procedure, the 204-byte packet can be Reed-Solomon decoded and returned to the original 188-byte packet form.
Generally, the conventional detection of the SYNC byte utilizes either of the following methods:
Firstly, the method of correlation is disclosed. The SYNC byte appears only once in each 204-bytes packet, and hence the correlation method searches for the SYNC byte in every possible position (204*8 bits).
Secondly, in the DVB-T standard, each OFDM block is regarded as an OFDM symbol, 68 symbols are regarded as a frame, and 4 frames are regarded as a super frame. Therefore, the first byte of each super frame is certainly a SYNC byte and can be identified as such.
The first conventional method requires complex arithmetic or hardware. Additionally, the first conventional method may incorrectly detect the SYNC byte. If the possibility of incorrect detection is to be reduced, data with a plurality of SYNC bytes has to be processed and which results in unnecessary time delays. The second conventional method has to wait for the first byte of the super frame, whose period may be 305 ms with 8k mode and ¼ guard interval. This also causes the worst case of 305 ms potential time delay in the second conventional method.
In addition, the DVB-T standard supports two transmission modes (2K mode and 8K mode), five puncture rates (such as ½, ⅔, ¾, ⅚, and ⅞), three constellations, and two hierarchy modes. Therefore, the transmitter needs to transmits a transmission parameter signal (TPS) to inform the receiver of the transmission mode, the puncture rate, the constellation, and the hierarchy mode so the receiver can operate correctly. In the DVB-T standard, the TPS is transmitted with a frame, where each OFDM symbol has one TPS bit, and a frame has 68 OFDM symbols, so each frame has 68 TPS bits in which to carry complete information. Please refer to FIG. 1 . FIG. 1 is a contrast table of the TPS bits and the carried information in the DVB-T standard. As shown in FIG. 1, the TPS utilizes 68 bits (S0-S67) to carry required information. As mentioned above, the receiver has to obtain completed TPS information to recover transmitted data correctly. The form of the TPS is known by those skilled in the art and the bit length of completed information is not large. If the information carried in the TPS and the relation between each TPS bit and symbol number can be further utilized to determine the SYNC byte, the disadvantages of the above-mentioned prior art methods can be avoided.